The present invention relates generally to communication systems, and specifically to methods and apparatus for transmission of cellular signaling, voice and other data over packet-switched networks.
Existing cellular communication networks are dependent on an infrastructure of circuit-switched wireline trunks. Typically, cellular operators maintain separate trunk networks for signaling, voice and other data. As cellular networks grow, the economic burden on the operators of maintaining or leasing these trunks becomes ever heavier. Communications among switches in a cellular network and between one cellular network and another must generally pass through switching equipment and lines belonging to public switched telephone networks (PSTNs), adding the expense of transfer fees to inter-network calls.
FIG. 1 is a block diagram that schematically illustrates a cellular communications system 20, as is known in the art. The system in this example includes two cellular networks 22 and 24, belonging to respective cellular operators xe2x80x9cCellco 1xe2x80x9d and xe2x80x9cCellco 2.xe2x80x9d The networks are connected to one another through a PSTN 26. A subscriber of network 22 communicates with a base transceiver station (BTS) 36 in the network using a mobile station (MS) 64. Typically, the BTS communicates with and is controlled by a base station controller (BSC) 34. When the user of MS 64 originates a call, appropriate signaling is sent from BTS 36 to BSC 34, and from the BSC to a mobile switching enter (MSC), 32. Typically, the signaling is in accordance with SS7 signaling specifications established by the International Telecommunications Union (ITU-T), as described in the Q.700 series of standards. The signaling to and from the MSCs is indicated in this figure and in other figures in this application by solid lines. Voice and other data communications are indicated by dashed lines.
Assuming that MS 64 initiates a call with another MS in another part of the network, say in communication with a MSC 28, MSC 32 sets up the call by sending a signaling message to a signaling transfer point (STP) 38 or 40. The STP sends the message on to MSC 28. The MSCs exchange messages through the STP in order to set up the call, and maintain this signaling link during the call for purposes of subscriber roaming, inter alia. Once the call is set up, a voice connection between MSC 32 and MSC 28 is established. In the present example, in which there is no direct voice line connecting MSC 28 and MSC 32, a third MSC 30 acts as a xe2x80x9ctandem,xe2x80x9d i.e., a circuit switch for conveying voice signals between the other two MSCs.
When the user of MS 64 wishes to make a call to a subscriber of network 24, MSC 32 must send a signaling message to STP 38 or 40 indicating that such a call is to be set up. The STP then signals an STP 44 or 46 belonging to PSTN 26, which signals an STP 48 or 50 in network 24, which finally signals the appropriate one of MSCs 54, 56 or 58 in network 24. Once the call is set up, MSC 32 transmits a voice stream from MS 64 through a tandem switch 62 in PSTN 26. The tandem switch passes the voice on to the appropriate MSC in network 24. In other words, the signaling and voice carried between networks 22 and 2 must pass through separate circuit switches (STPs and tandems) of PSTN 26, with charges levied by the PSTN for both.
A further feature of many cellular networks is a short message service (SMS), provided by a SMS center 42 or 52. The SMS enables network subscribers to send data messages to other subscribers. These data messages are normally carried over the signaling (solid) lines in the cellular network. The popularity of SMS is creating a growing burden on the cellular signaling infrastructure.
Generally speaking, because cellular networks have been developed primarily for circuit-switched transmission, they are not well suited for packet-switched data. For this reason, the European Telecommunications Standards Institute (ETSI) has proposed a general packet data service (GPRS) to operate in conjunction with Global System for Mobile (GSM) cellular networks. When a MS in a GSM network with GPRS wishes to send and/or receive packet-switched data, the MS makes contact with a xe2x80x9cserving GPRS support nodexe2x80x9d (SGSN not shown in the figures) through the BSC with which the MS is in communication. The packet data are transmitted and received by the BSC through the SGSN, separately from the voice channels that go through the MSC. The SGSN is connected to a packet data network, such as the internet, rather than to the existing cellular and PSTN infrastructure. The SGSN likewise maintains its own separate mobility management and security facilities. Implementation of GPRS requires a substantial investment in new network infrastructure, and users must have suitable, GPRS-compatible MSs. The GPRS can also be used to carry SMS messages by xe2x80x9ctunnelingxe2x80x9d over the packet data network.
Solutions are becoming available for enabling MSCs to exchange voice, as well as data, over packet-switched links, in place of the circuit-switched links in traditional cellular networks. For this purpose, a packet gateway, such as the AS5300 Voice-over-internet-Protocol (VoiP) gateway, produced by Cisco Systems (San Jose, Calif.), can be coupled to the MSC voice output. Signaling, however, is still conveyed over existing circuit-switched lines. In order to set up a new call, the MSC signals one or the STPs, just as described above with reference to system 20. The signals are then sent to the packet gateway, in order to control transmission of packet data to a corresponding gateway at another MSC that receives the call. While enabling communications between MSCs to be routed over packet-switched links, this solution greatly complicates the cellular signaling network.
As an enhancement to this concept, a central signaling gateway is added at the STP to receive the signals sent by the MSC. An example of a signaling gateway of this sort is the Signaling Gateway USP, produced by Nortel Networks (Saint John, New Brunswick). The signaling gateway invokes a media gateway controller to take over the function of call set-up from the MSC, which is normally responsible for this function in conventional cellular systems. During call setup, the media gateway controller directs a media gateway at the MSC site, such as the above-mentioned AS5300 device, to set up connections over a packet-switched link to the media gateway at the receiving MSC site.
It is an object of the present invention to provide improved apparatus and methods for conveying communications signaling, and particularly cellular and other SS7 -based signaling over packet-switched networks.
It is a further object of some aspects of the present invention to provide apparatus and methods for convergence of cellular signaling, voice and data over a common network, in particular a packet-switched network.
It is yet a further object of some aspects of the present invention to enable existing cellular equipment, particularly existing MSCs, to convey signaling over packet-switched links while minimizing the changes required in the cellular equipment for this purpose.
In preferred embodiments of the present invention, an integrated packet-switching gateway is coupled to a cellular network switch, typically to a MSC. The switch is normally adapted and programmed, in the absence of the gateway, to communicate with other switches in the cellular network over circuit-switched links, as is known in the art. The integrated gateway, however, converts the signaling, voice and other data output by the switch to packets, and routes the packets over a common packet-switched network to other switches in the cellular network. Similarly, the gateway receives packets sent from other switches over the packet-switched network and passes them to the appropriate inputs of the cellular network switch, which sends and receives signaling, voice and other data through the gateway as though it were communicating over a standard, circuit-switched link.
By providing convergence of the signaling, voice and other data over a common packet-switched network, the integrated gateway simplifies and reduces the costs of communications among the cellular network switches. Vis a vis the switch, however, the gateway emulates the circuit-switched links of the conventional cellular network, so that this convergence is achieved substantially without modification to the existing cellular infrastructure. The packet-switched links established between the gateways of the present invention are preferably used both for communications between switches within a given cellular network and for communications between one cellular network and another. The use of these gateways thus enhances the scalability of the cellular network and reduces the costs to cellular operators of wireline infrastructure and transmission through PSTN switches, allowing the cellular network instead to use lower-cost packet network infrastructure.
Preferably, the integrated packet-switching gateway comprises a control unit and a media gateway unit. The control unit performs the functions of a signaling gateway and of a media gateway controller. As noted above, in preferred embodiments of the present invention, the entire integrated gateway is located at the site of the cellular network switch and works closely in conjunction with the switch itself, unlike signaling gateways known in the art. Control of call connections is thus maintained at the MSC level, avoiding the added complication of transferring this function to a centralized media gateway controller. The local control unit also performs the function of media gateway control. Alternatively, the control unit by itself (without a media gateway) is used at the cellular network STPs to provide packet-switched links with other STPs and with the MSCs in the network. The gateway also preferably comprises a router, most preferably an Internet Protocol (IP) router, which receives both the signaling packets from the control unit and the voice and other data packets from the media gateway unit and routes them over the packet-switched network to the appropriate target gateway.
As noted. above, the packet-switching gateway of the present invention handles both signaling and voice, as well as other data communications. All of these communication types are passed through the packet-switched network in the form of packets, regardless of their contents. Therefore, in the context of the present patent application and in the claims, the term xe2x80x9cpacketxe2x80x9d is to be understood as referring to signaling, voice and/or data packets, unless otherwise specified. Furthermore, the terms xe2x80x9cmediaxe2x80x9d and xe2x80x9cdataxe2x80x9d are to be understood generally as including voice and other audio data, in addition to other types of data and media generated in communications between computers or other data devices.
There is therefore provided, in accordance with a preferred embodiment of the present invention, gateway apparatus for coupling a cellular switching center to a packet-switched network, including:
a control unit, adapted to receive upstream signaling messages from the cellular switching center destined for a cellular signaling transfer point or for another cellular switching center and to packetize the messages for transmission over the packet-switched network; and
a media gateway unit, adapted to receive from the cellular switching center upstream media data and to packetize the media data for transmission over the packet-switched network.
Preferably, the media data include voice signals. Alternatively or additionally, the media data are generated by a computer in communication with the cellular switching center.
Preferably, the media gateway unit and the control unit are located at a site of the cellular switching center from which they respectively receive the media data and the signaling messages. further preferably, the control unit is further adapted to receive message packets from the packet-switched network and to generate, responsive to the message packets, downstream signaling messages for delivery to the cellular switching center.
In a preferred embodiment, the control unit and the media gateway unit are adapted to packetize the signaling messages and the media data, respectively, in accordance with the Internet Protocol (IP). Preferably, the apparatus includes an ID router, which is coupled to route the packetized messages and data over the network. Further preferably, the control unit is adapted to extract routing information from the signaling messages received from the cellular switching center and to determine an IP address to which to send the packetized messages based on the routing information. Most preferably, the routine information includes Message Transfer Part (MTP) 3 and/or Signaling Connection Control Part (SCCP)/Global Title Translation (GTT) information. Additionally or alternatively, the packet-switched network includes a local area network (LAN) linking the control unit and the media gateway unit. Preferably, the control unit includes a media gateway controller, which is coupled to control the media gateway unit via the LAN. Further additionally or alternatively, the packet-switched network includes a wide-area network (WAN), coupled to the LAN so as to enable the cellular switching equipment to communicate via the WAN with other cellular switching equipment, with a router that is configured to couple the WAN to the LAN.
Preferably, the control unit is configured to emulate circuit-switched signaling communications between the cellular switching center and other elements of a cellular network. Typically, the cellular switching center includes a mobile switching center (MSC), and the control unit is configured to emulate the signaling communications between the MSC and the signaling transfer point in the cellular network. Alternatively or additionally, the control unit may be configured to emulate a Home Subscriber Service (HSS), a Home Location Register (HLR), a Service Control Point (SCP), an Equipment Identity Register (EIR), and/or a Short Message Service (SMS) center. In a preferred embodiment, the control unit is adapted to select for packetizing certain of the signaling messages that are to be transmitted over the packet-switched network, while other signaling messages are transmitted by the cellular switching equipmen: over a circuit-switched link.
Preferably, the signaling gateway is adapted to receive the signaling messages in accordance with a predetermined call control protocol of the cellular network and to pass the messages over the packet-switched network substantially without termination of the call control protocol. Most preferably, the control unit is further adapted to track or monitor a state of a call placed by the cellular switching center without termination of call-related and trunk maintenance signaling, and to control the Media Gateway. Additionally or alternatively, the control unit is adapted to read a destination field in the signaling messages and to transmit the messages to a destination address on the packet-switched network corresponding to the destination field. Most preferably, the signaling protocol includes a SS7 protocol, and wherein the destination field includes a destination point code. Additionally or alternatively, he control unit is further adapted to track or monitor a state of a call placed by the cellular switching center, and to control the media gateway unit responsive to the state of the call.
Preferably, the packet-switched network couples the cellular switching center, via the gateway apparatus, with other cellular switching equipment within a common network. Additionally or alternatively, the cellular switching center belongs to a first cellular network, and wherein the packet-switched network couples the cellular switching equipment, via the gateway apparatus, with cellular switching equipment in a second cellular network.
In a preferred embodiment, the control unit is further coupled to receive data messages from a cellular short message service (SMS) and to packetize the data messages for transmission over the packet-switched network.
In other preferred embodiments, the control unit is further coupled to receive data messages from a cellular Home Location Register (HLR), a cellular Equipment Identity Register (EIR), a Service Control Point (SCP), and/or a cellular third generation (3G) Home Subscriber Server (HSS), and to packetize the data messages for transmission over the packet-switched network.
There is also provided, in accordance with a preferred embodiment of the present invention, cellular communications apparatus, including:
a plurality of cellular network switches, each switch adapted to transmit and receive signaling messages and media data; and
plurality of integrated gateways, at least one such gateway associated with each of the plurality of network switches and coupled to receive the signaling messages and media data transmitted by the associated switch adapted to convey the messages and data together over a common stream or link to another of the gateways associated with another one of the network switches.
Preferably, the common communication link is part of a packet-switched communication network. Most preferably, the gateways are adapted to packetize the signaling messages and media data for conveyance over the packet-switched communication network in accordance with the Internet Protocol (IP). Preferably, the cellular network switches are configured to communicate, in the absence of the gateways, over connections in a circuit-switched network, and the integrated gateways are configured to emulate circuit-switched communications with the associated cellular network switches. Further preferably, the integrated gateways share a common address in the circuit-switched network. Most preferably, the switches are configured to transmit the signaling messages in accordance with a SS7 signaling protocol, wherein the plurality of integrated gateways have a common SS7 point code.
In a preferred embodiment, the apparatus includes a signaling transfer point (STP) and a signaling gateway associated with the STP, which is configured to exchange signaling messages over the common communication link with the gateway associated with the at least one MSC.
There is additionally provided, in accordance with a preferred embodiment of the present invention, a method for coupling cellular switching equipment to a packet-switched network, including:
receiving upstream signaling messages and upstream media data from the cellular switching equipment; and
packetizing the messages and the data for transmission over a common stream or link in the packet-switched network.
Preferably, packetizing the media data includes controlling a media gateway which packetizes the media data in accordance with information derived from the upstream signaling messages. Most Preferably, controlling the media gateway includes monitoring a state of a call in accordance with a SS7 ISDN User Part (ISUP) protocol, and controlling the media gateway responsive to the monitored state.
Further preferably, receiving the signaling messages and the media data includes mimicking circuit-switched signaling communications between the cellular switching equipment and other elements of a cellular network. Most preferably, the cellular switching equipment comprises a mobile switching center (MSC), and mimicking the circuit-switched signaling communications includes mimicking signaling communications between the MSC and a signaling transfer point (STP) in the cellular network or between the MSC and another MSC in the cellular network, wherein packetizing the messages includes sending the messages over the packet-switched network from a first integrated gateway to a second integrated gateway, both gateways having a common point code in the cellular network.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: